1. Field of the Invention
The present invention relates generally to sorbent tube sampling devices for determining the nature and quantity of chemical and biological contaminants in air and other gases, and particularly to a encapsulated sorbent tube which has a frangible encapsulation element and which is independent of and protective of a sampling sorbent tube contained therein.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97-1.99
There is a large and continuing need for identifying and monitoring the level of pollutants or contaminants in air and in industrial gas streams. This need is often addressed by obtaining a sample of the air at the monitoring site and transporting the sample to a laboratory for analysis. Samples may be obtained by manually filling a sampling container such as a plastic bag, a hypodermic syringe, or an evacuated metal or glass vessel, and sealing it for transportation. However, sampling devices that take a bulk air sample for transport and later analysis are often inappropriate for use in circumstances in which the contaminant being monitored is present in small concentrations, in the parts per billion or even parts per trillion range. The size of the sample that is collected is often too small for the contaminant to be detected and its concentration measured. That requirement has led to the development of sampling devices that preferentially extract and trap the contaminants from the sampled air or gas stream and hold the trapped contaminant for later release and analysis. Sampling sorbent tubes are among such devices as the tube contains a sorbent material that functions to extract and hold contaminants from an air stream passing through the tube. Because most contaminants of interest are organic compounds, the sorbent material is chosen to absorb those compounds while allowing air and inorganic compounds to pass through the tube substantially unimpeded. There exist a variety of thermal desorption or sampling sorbent tubes which are used to extract and retain volatile organic compounds from air flowing through them during the sampling period for later analytical determination of the volatile organic compounds contained in the air. When such sampling sorbent tubes are loaded onto an analytical instrument, the retained volatile organic compounds are liberated using thermal desorption and allowed to flow into the analytical instrumentation. Analysis of the liberated volatile organic compounds is then accomplished using any of several analytical instruments or using a combination thereof.
The foregoing sampling sorbent tubes require that the tube be maintained in a contaminant-free condition prior to air sampling at the monitoring site. In this regard, the sampling sorbent tube may be manufactured to have a body portion internally containing desired sorbent material and lateral end portions that are either capped with plastic over-caps or screw threaded end caps. Alternatively, the sampling sorbent tube itself may be formed to be of an integral closed construction having its lateral ends enclosed for a later breakage by a user at a monitoring site to then expose the central body portion containing the desired sorbent material.
In the former case of capped sampling sorbent tubes, the capping of open sorbent tube ends may not form a perfect, airtight seal and, therefore, may permit the exchange of surrounding air with the air inside the sampling sorbent tube. Any volatile organic compounds contained in the air passing into the thermal desorption tube during storage and/or transport to a monitoring site are adsorbed onto the sorbent contained therein and are, during the subsequent analysis, desorbed into the analytical instrument and are manifest as interferences, background, or sample overlap. Because of these deleterious analytical interferences or the potential thereof, the amount of time that capped sorbent sampling tube can be stored prior to actual monitoring site use is greatly reduced. In addition, the user is afforded no assurance that the thermal desorption tube has been stored in a clean environment and is free of contamination.
In the latter case of the sampling sorbent tube itself being formed with integral closed ends for later breakage to expose a central body portion of the tube at a monitoring site, such sampling sorbent tubes are designed to be disposable being suited for one time usage due to the structural integrity of the tube itself being damaged by breakage of their ends to achieve exposure of the central body portion of the tube. Since the sampling sorbent tube must be broken near its sealed ends, it necessarily is of a thin walled construction to permit such breakage. However, such a construction may make the sampling sorbent tube itself more prone to mechanical damage during shipping and handling. Still further, as the sampling sorbent tube itself is damaged during breakage of its sealed ends, a user may be exposed to glass shards at a breakage site which may injure the user. In addition, the break may produce crack initiation lines that may propagate into the useable body portion of the sampling sorbent tube compromising its integrity thereby diminishing or threatening its usefullness.